Infectious agents generally have their first contact with host organisms at a mucosal surface. Therefore, mucosal protective immune mechanisms are of key importance in preventing these agents form colonizing or penetrating the mucosal surface. It is apparent from past studies that a protective mucosal immune response can best be obtained by introduction of the antigen at the mucosal surface; however, parenteral immunization has not been an effective method to induce mucosal immunity. Antigen taken up by the gut-associated lymphoid tissue (GALT), primarily by the Peyer's patches stimulates T helper cells (TH) to assist in IgA B cell responses or stimulates T suppressor cells (TKS) to mediate the unresponsiveness of oral tolerance.
While particulate antigen appears to shift the responses towards the (TH), soluble antigens favor a response by the (TKS).
Although studies have demonstrated that oral immunization does induce an intestinal mucosal immune response, large doses of antigen are generally required to achieve sufficient local concentrations in the Peyer's patches. Further, unprotected protein antigens tend to be degraded or they complex with secretory IgA in the intestinal lumen.
One approach to overcoming the aforementioned problems is to homogeneously disperse the antigen of interest within the polymeric matrix of biodegradable, biocompatible microspheres that are specifically taken up by GALT. Eldridge, et al.1 have used a murine model to show that orally-administered 1-10 micrometer microspheres consisting of polymerized lactide and glycolide, (the same materials used in resorbable sutures), were readily taken up into Peyer's patches, and that 1-5 micrometer sizes were rapidly phagocytized by macrophages. Microspheres that were 5-10 micrometers (microns) remained in the Peyer's patches for up to 35 days, whereas those less than 5 micrometer disseminated to the mesenteric lymph node (MLN) and spleen within migrating MAC-1+ cells.
1Biodegradable Microspheres: Vaccine Delivery System For Oral Immunization, 1989, 146. 
However, Eldridge, et al. used 50 μm microspheres of poly (DL-lactide-co-glycolide) composed of molar parts of polymerized lactide and glycolide (85:15 DL-PLG), which biodegrades to completion in approximately 24 weeks after intramascular injection.
Poly (DL-lactide-co-glycolide) composed of equal molar parts of polymerized lactide and glycolide (50:50 DL-PLG) is the more stable or lest biodegradable, and biodegrades to completion after 25 weeks.
Therefore, there is a need extant in the biodegradable microsphere field to provide a method of producing poly (DL-lactide-co-glycolide) materials of 50:50 DL-PLG that is more biodegradable and capable of being taken up by both M cells and non-M cells in the Peyer's patches follicle-associated epithelium when used as microencapsulant as carriers for antigens for enteric immunization.